1. Virus and Prion Research Unit; National Animal Disease Center; USDA-ARS; Ames IA USA
2. Fogarty International Center; National Institutes of Health; Bethesda MD USA
3. National Veterinary Services Laboratories; USDA-APHIS; Ames IA USA
4. Centers for Epidemiology and Animal Health; USDA-APHIS; Riverdale MD USA